Broadcast solution for cable IPTV

ABSTRACT

Methods and apparatus are disclosed for offering broadcast IPTV solutions over cable (HFC networks). Rather than bypass the CMTS, a reduced number of downstream ports are utilized for video streams. Each input video stream is streamed to a multicast group address. In one embodiment, several RF channels are configured so that they are RF spanned across all the Fibernodes in the CMTS service area. In an embodiment, an STB sends a service request for a desired video stream using an IGMP request, and the CMTS responds by issuing a DBC request to tune the corresponding CM to the RF channel that is carrying the requested stream. Preferably, the CMTS ports that carry the static multicast streams are RF spanned across all the Fibernodes, or a selected subset.

TECHNICAL FIELD

The present disclosure relates generally to the field of cable networks,and more specifically to distribution over cable networks ofvideo-on-demand, IPTV broadcasting, and other forms of streamingmultimedia content.

BACKGROUND

Selected Acronyms

CM Cable Modem

CPE Customer Premises Equipment (connects to CM)

CMTS Cable Modem Termination System (maybe integrated or modular)

DOCSIS Data Over Cable Service Interface Specification

DSBG Downstream Bonding Group

DSID Downstream Service Identifier

CMCI-Port Physical interface to which CPE can attach to a CM

IGMP Internet Group Management Protocol (IPv4)

PCMM Packet Cable Multimedia

Data Over Cable Service Introduction

Cable operators have widely deployed high-speed data services on cabletelevision systems. These data services allow subscriber-side devices,such as personal computers, to communicate over an ordinary cable TVnetwork Hybrid Fiber Coax (HFC) cable. Cable Television Laboratories,Inc. (CableLabs®) publishes detailed technical specifications for suchsystems, including DOCSIS—Data Over Cable Service InterfaceSpecification. Referring to FIG. 1, in a cable system 100, a Cable ModemTermination System (CMTS) 102 (or a modular CMTS called “M-CMTS”)connects the cable network 104 to a data network, such as the Internet106. In a modular CMTS architecture the DS MAC and PHY are separated,with the MAC residing in the M-CMTS core and the DS PHY being a part ofthe external EQAMs. (Some systems may utilize a Universal Edge QAMdevice, or “UEQAM” for short, which typically comprises a chassis havingone or more gigabit Ethernet (GigE) input ports, and multiple QAMmodulators and RF upconverters on the output (downstream) side.) Adownstream QAM 110 receives data transferred from the CMTS over a packetswitched portion of the network, performs modulation and otherprocessing, and then transfers the modulated data over a Hybrid FiberCoaxial (HFC) portion 120 of the cable network to subscribers. This iscalled the “downstream” direction.

In general, this HFC or coax cable feeds the last link (for example,over the last half mile or less) to an individual home or otherstructure. There, a cable modem (CM) 130 may provide a packet interface,for example Ethernet compliant, to various consumer premises equipment(CPE) 132 such as a personal computer. The CM may be connected to a hubor router (not shown), for example to implement a home network, wirelessaccess, etc. The CM (or a second CM) may be implemented in otherequipment, for example a “set-top-box” (STB) 140 which provides aninterface to a television or other video display 142. A CM may servemultiple subscriber devices or “clients” on separate interfaces.

DOCSIS specifies that the cable modems obtain upstream bandwidthaccording to a request/grant scheme because the upstream channel isshared. A cable modem sends a bandwidth allocation request when itreceives a packet from a subscriber device and the packet needs to besent upstream into the cable network. The CMTS scheduler grants theserequests using bandwidth allocation map (“MAP”) messages. MAP messagesinform the CMs about specific allocations of upstream spectrum in thetime dimension, using time slots or “minislots.” The requesting modemthen waits for its scheduled time before it can begin transmission. Inthis way, the system avoids collisions in upstream transmissions frommultiple CMs.

In addition, individual CMs are assigned to specific frequency“channels.” In this way, more than one CM may actually transmit at thesame time, but they are separated by frequency division multiplexing.DOCSIS 3.0 allows a single CM to transmit on multiple upstreams(channels), as further discussed below. In other words, a DOCSIS 3.0enabled CM may have multiple transceivers simultaneously operable atdifferent frequencies. In some newer wideband CMs, a single transceivermay be tunable over multiple channels, within a given frequency range.DOCSIS 3.0 CM operate on at least four frequency channels concurrently.

Recently, especially in newer communities, service providers (ordevelopers) are implementing fiber to the home (FTTH), in other words,running “fiber” or “glass” (optical fiber cable) all the way from thehead and or distribution hub to the home. FTTH is desirable because itcan carry high-speed broadband services integrating voice, data andvideo. Accordingly, separate traditional telephone lines (copper) may nolonger be necessary. And coax to the home for internet access andtelevision programming may be obviated as well. RF over Fiber (“RFoG”)is advantageous because the analog RF signals transmitted over fiber (inthe form of photons) incur little loss, even over run lengths of manymiles, whereas losses over coax can be significant, requiring the use ofrepeaters or amplifier equipment every 1000 to 2000 feet. Fiber is alsoessentially immune to EM interference and unauthorized eavesdropping. Inmany existing systems, fiber runs only to a “Fibernode,” from whichpoint coax is used for the remaining segment to individual homes oroffice.

Television and Other Streaming Video

Cable networks such as those described above have been widely deployed.Many households and businesses rely on cable modem connectivity foremail and other Internet access. And many customers enjoy televisionprogramming delivery via the cable networks. “Cable TV” today comprisesforwarding of both analog and digital broadcast television, as well ascable stations, i.e. stations that broadcast only via the cable network(as well as radio programming and some other services). The use ofdigital protocols such as IP (Internet Protocol) for streaming videocontent offers significant benefits. Among them is the ability toprovide “IPTV” service in which a customer can select among a menu ofdigital TV stations or other digital content as explained below.

Several preferred examples of the present invention will now bedescribed with reference to the accompanying drawings. Various otherexamples of the invention are also possible and practical. Thisapplication may be exemplified in many different forms and should not beconstrued as being limited to the examples set forth herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram illustrating a DOCSIS network.

FIG. 2 is a simplified block diagram illustrating an RF over glassnetwork.

FIG. 3 is a simplified block diagram illustrating an IPTV over cableimplementation.

FIG. 4 is a simplified flow diagram illustrating selected aspects of aprocess for providing IPTV services over a cable plant.

FIG. 5 is a simplified block diagram of a cable system networkarchitecture arranged for delivery of IPTV services.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The figures listed above illustrate examples of the application andoperation of aspects of the invention. In the figures, the size of theboxes is not intended to represent the size of the various physicalcomponents. Where the same element appears in multiple figures, the samereference numeral is used to denote the element in all of the figureswhere it appears. When two elements operate differently, differentreference numerals are used regardless of whether the two elements arethe same class of network device. Only those parts of the various unitsare shown and described which are necessary to convey an understandingof the examples to those skilled in the art.

To illustrate one example of an operating environment suitable for thepresent invention, a simplified FTTH network is described next, by wayof illustration rather than limitation, with reference to FIG. 2. A QAM212 of CMTS 210 is coupled to an RFoG Headend Interface (“RHI”) 222 forconverting the RF signals between coax and glass media; in other words,it provides an interface from coax to the passive optical network (PON)220. At least one fiber 223 is coupled to the downstream side of the RHI222. Fiber 223 may be coupled to a passive optical splitter 224. Forexample, splitter 224 may couple or “split” the signal from fiber 223into, for example, 32-128 individual fibers 228, 238 (only two areshown). The splitter may be passive. It is bidirectional, acting as acollector or aggregator in the upstream direction, as further discussedlater. In typical systems, an RHI is composed of an optical transmitterand EDFA (Erbium-Doped Fiber Amplifier) for downstream, an opticalreceiver for upstream, and a shared WDM module.

Downstream from the splitter, PON 220 may include one or more usernodes, called optical network units (ONUs). In FIG. 2, fiber 228 iscoupled to Optical Networking Unit ONU 230, and fiber 238 is coupled toONU 240. Each ONU may serve an individual home or building. In someembodiments, the ONU may serve on the order of 50 subscribers. Ingeneral, an ONU is a single integrated electronics unit that terminatesthe PON and converts optical signals to electronic signals on coax. Itis also referred to as a “fiber node”. The ONU typically will havelittle or no local “intelligence.” The ONU may be located at a junctionbox, for example, on the outside of a building, in newer construction.Or, it may serve a group of houses.

A subscriber premises may have a cable modem (CM) 232, which in turnserves various attached customer premises equipment (CPE) 236, such as acomputer, wireless router, etc. In another arrangement, a CM may beimplemented in a set-top box (STB) 234, or otherwise coupled to an STB,as further discussed below, for delivery of video services such as IPTV.A television 235 is shown connected to the STB 234 for display ofreceived video content.

In native MPEG deployments, most solutions are broadcast typearchitectures. All of the TV video streams would be carried all the timeon a set of RF channels. (A single RF channel may carry several TV videostreams.) The STB would tune to the RF channel where a desired TV steamcould be found. Such MPEG deployments while well-suited to deliver videoto traditional digital cable set-top-boxes, are not directly capable ofconnecting to IP end devices, such as PCs, hand-held devices and IPSTBs.Solutions of that type, however, occupy large amounts of spectrum.

FIG. 3 is a simplified overview illustration of elements of a cablenetwork that provides IPTV (as well as other types of services). Here, aCMTS 300, as discussed earlier, includes at least one EQAM 304, fortransmission over the HFC network 306 to subscribers. A CM 310 includesmultiple transceivers 312, and one transceiver 314 dedicated to IPTV.Having one tuner reserved for IPTV is preferred but not a requirement,as further explained below. A set-top box (STB) 320 is coupled to, orincludes, the CM 310. Finally, a television 330 is connected to the STBas before. The STB 320 enables a user, via front panel or remotecontrol, to select desired video programming for display on thetelevision. (The STB may have other functions as well, not pertinenthere.)

In an embodiment, the STB enables “station” selection, for example bycable service “channel number” (typically a two or three digit integer),or call letters (“KATV” “KOIN”) or other well-known video broadcastsource identifiers (“ESPN” “CNN” “OPB” etc.) or some combination ofthese identifiers. Content from each of these sources is delivered tothe cable network as a unique IPTV stream. Referring again to FIG. 3,these input streams 402, 404 for example, may be provided to the CMTS300 via an IP network, or any other suitable packet-switched protocol.The CMTS typically maintains a database, lookup table, or the like,illustrated at 410, which stores the corresponding multicast groupaddress for each input stream. In addition, the CMTS assigns an RFchannel to each stream, as further explained below.

In one embodiment, the STB 320 maintains a database, lookup table, orthe like (not shown), that stores the correspondence between the popularstation identifiers (“ESPN” etc.) and the corresponding video streammulticast group address. This information is used, as explained below,for the STB to request the programming selected by a user for recordingor display. In some embodiments, the STB may acquire or update theprogramming-to-multicast address mapping via a middleware application.In an embodiment, the STB or other subscriber equipment may request anentire mapping of available streams, or an update of the mapping, orjust the mapping for one or more specific streams. In anotheralternative, these mappings may be predetermined, and stored in memory,or downloaded from a third party resource such as a website in advanceor in real time.

Referring now to FIG. 5, a simplified block diagram illustrates oneexample of a cable system network architecture suitable for delivery ofIPTV services. Here, a hub 500 may includes several CMTS's. Forillustration, only one CMTS 504 is shown. The CMTS 504 is coupled to anIP Network 506 for IP data communications (using data in its broadestsense). An video-on-demand (VOD) and or SDV (Switched Digital Video)server or “back office” 510 may be coupled to the IP Network to providecorresponding services to the hub. Other multicast video sources 512 maybe coupled to the IP network as well. These sources may include one ormore of various encoders, ad-insertion equipment, satellite receivers,statistical multiplexers or local encoders. A VOD server may provideunicast video sources. (A modular CMTS is shown but an integrated CMTScan be used as well.)

The CMTS 504 is coupled to an edge QAM or EQAM 508. Typically, a CMTSmay have 40 downstreams, although the specific number is not criticalhere. For illustration, we indicate them as downstreams f1 through fm.In operation, each of the TV streams that need to be offered (e.g. fromsources 512) will be streamed to a multicast group address. In oneembodiment, one or more RF channels are configured on the CMTS such thatthey are “RF spanned” across all the Fibernodes served by the CMTS. Inother words, the selected RF channels are split to all the Fibernodesserved by the CMTS so that they can potentially reach all of thesubscribers served by the CMTS. Typically, each CMTS might serve 40Fibernodes.

In another embodiment, the downstreams may be RF spanned across one ormore subsets of the Fibernodes served by the CMTS. For example the FNsserved by a CMTS may belong to multiple ad-zones. So different FNsshould receive different copies of the stream. Thus CNN itself may beavailable on two different multicast addresses, each with different Adson it, and these can be spanned across an appropriate subset of theFibernodes. In an embodiment, there may be multiple sets of RF channelsthat are each RF spanned across a different subset of FNs served by theCMTS.

A downstream channel (DS) has, e.g., around 38.8 Mbps of bandwidth. Thedownstream channel is transmitted by a QAM port. Each channel is definedby a predetermined frequency and related parameters. Multiple inputstreams (video streams) (402 in FIG. 3; from IP Network 506 in FIG. 5)may be assigned to each DS. For example, a typical input stream may havea bandwidth of 2 or 3 Mbps. So, depending on the selected streams, theremay be on the order of 5 or 10 input streams (multicast streams) on eachdownstream channel. This number can vary and may be larger. Thus thetotal number of RF channels required at a given time will depend on thenumber and bitrates of the TV streams.

In some architectures the CMTS may carry all TV input streams via staticmulticast, or using a combination of static and dynamic, for example,where the most popular content is configured to be carried staticallywhile the less popular content is carried dynamically. Here we areconcerned with the static multicast streams. Thus all of the streams ofinterest are typically statically multicast on the assigned RF channels.Although described in the context of static multicast streams, theinvention is also applicable to dynamically multicast streams. If theset of downstreams are RF spanned across a large number of FNs, thegains of using dynamic multicast over static multicast may be minimal.Next we describe delivery of the requested programming streams toindividual subscribers in some preferred embodiments.

Referring again to FIG. 5, a CM 522 in a household that has subscribedto the IPTV service typically will have at least one tuner dedicated toIPTV. (It is possible in alternative embodiments that only when anendpoint device requests a video stream does a CM tuner become dedicatedto video. Otherwise that tuner could also be used for data. Dynamicallybased on a video request, the CMTS could remove this tuner from HSDservice and use it for video.) Depending on the program request from theSTB 524, this tuner will be moved to the appropriate frequency, i.e.,the channel that contains the requested program stream. In a presentlypreferred embodiment, the STB sends an IGMP request, for the programselected by the subscriber or user. On receiving the IGMP request, theCMTS identifies the RF channel that is carrying the requested multicaststream. For example, in FIG. 3, the STB 320 sends an IGMP request 322 toCMTS 300. The CMTS conducts a lookup in datastore 410 and determines theassigned channel for the requested stream. This can be done using themulticast group address provided by the STB in the request message.

In response, the CMTS then issues a DBC (Dynamic Bonding Change) Requestmessage to the CM. The CMTS changes the Receive Channel Set (RCS) of theCM to include the identified channel corresponding to the streamrequested by the STB. (Typically, the CMTS lists the complete set offrequencies the CM must tune to, although only a single frequency isbeing changed.) The CM then tunes to the new frequency received via DBC,and forwards the requested multicast stream to the STB. In anembodiment, the CM supports MDF enabled mode, i.e., multicast DSIDforwarding. For example, the STB reads the packet headers and selectsthose having the multicast group address that corresponds to the streamselected by the user. The STB processes the stream and delivers thecontent to the television or other CPE. Although we refer to an STB isthis description, other devices with similar functionality may be used.In general, the “endpoint” may be a PC, for example, a hand-held deviceor any other IP device capable of consuming video. For example, ahand-held device such as an iPod® or Blackberry® may be coupled to a CMvia a wireless router.

FIG. 4 is a simplified flow diagram illustrating the foregoing process.In FIG. 4, CMTS activities are generally shown on the left side, and CMactivities are shown on the right. Details are omitted to not obscurethe broader concepts of this embodiment. As mentioned, various videoinput streams are available to the CMTS, illustrated at block 402.During the usual CM registration procedures, block 404, the subject CMreports its MDF (Multicast DSID Forwarding) capability, 406, and it isconfigured with MDF enabled mode, 408. This feature may be used tofilter and forward video stream packets to the appropriate client of theCM. The CMTS, as explained, configures RF channels to span selectedinput streams across selected fibernodes, block 430.

When a user at the customer premises selects a desired video source,block 410, for example using an STB, the STB generates an IGMP requestmessage, and the CM passes that message upstream to the CMTS, block 412.The message is received at the CMTS, block 414, and the CMTS identifiesthe RF channel to which the requested input stream had been assigned.The CMTS then issues a DBC request message directed to the requestingCM, see block 420, and the CM, upon receiving the request, configuresits receivers/tuners as requested so as to include the appropriatechannel, block 422, to receive the requested stream. In block 450, theCM provides filtering and forwarding the received packets to therequesting endpoint.

Preferably, the CM also supports channel bonding. For example, FIG. 5illustrates a first service group SG #1 550 that includes, forsimplicity, two subscribers. A first subscriber is associated with a4-channel CM 552, and that user subscribes to HSD service only. Abonding group BG#1 consists of four channels (f1-f4) and may serve thatCM 552. The first subscriber is not a TV subscriber, so no tuner is usedfor TV reception. Another bonding group BG #2 illustrates use of threebonded channels f1-f3.

Additional downstreams f5-fm from EQAM 508 may be RF spanned acrossmultiple service groups SG #1 to SG #n 580. These may span across someor all of the Fibernodes served by the CMTS. Video streams may beassigned in various configurations. For example, streams 1-20 on channelf5, streams 21-40 on channel f6, etc. In some cases, channels may bebonded to deliver more or higher bandwidth steams. For, illustration, asecond subscriber, also in SG #1 (but not necessarily so) is associatedwith CM 522 which in turn is implemented in, or coupled to, an STB 524.At least one tuner in the CM is dedicated to video, which in the case ofa 4 channel CM would leave three channels available for HSD services. Ingeneral, any CM in any of the SG's could tune to one or more of the IPTVchannels as described herein to receive requested IPTV video streams.This is just one example of using multiple tuners. Variousconfigurations may be used, depending on the number of streams,bitrates, number of CM tuners, etc.

In some embodiments, one tuner on the CM may be dedicated to video. Thisreduces the number of tuners available to HSD service. To avoid thislimitation, bonding groups may be configured, for example, to provide a3-channel BG for HSD for those CMs that have subscribed to HSD+IPTV(assuming a 4 channel CM), and a 4-channel BG for HSD for those CMG thathave subscribed to HSD service only. In that way, while one tuner isdedicated to IPTV, the HSD-only users will have all four channelsavailable to HSD bandwidth. In another embodiment, all subscribers mayhave a common size of bonding group for HSD, say 3 channels. In someembodiments, two or more channels may be dedicated to IPTV. Thesechannels may be received via one or more receivers or tuners.

Above we described a single video stream per home using one dedicatedtuner for video, in another embodiment two or more video streams per CMmay be supported. this may be implemented, for example, using multipleagile tuners in the CM or having block tuners with wide capture windows.Various alternatives are contemplated depending on the specific CM andnumbers of transceivers and tuners available at the subscriber premises.

Video Streams

In general, each of the multicast streams may be a carried as a MPEGtransport stream in the payload of a UDP/IP packet. Typically thestreams will be Constant Bit Rate (CBR), but they could also be carriedas Variable Bit Rate (VBR), which are 30-40% more bandwidth efficientthan CBR streams. In the case of VBR streams, an encoder/statisticalremultiplexer (see 512 in FIG. 5) preferably would ensure that theaggregate bandwidth of the video streams is less than the bandwidth of asingle RF channel. To provide a good user experience, the channel changetime preferably should be as small as possible. Toward that end, theCMTS should be arranged so as to process IGMP requests and issueappropriate DBC messages relatively quickly. For example, a searchalgorithm to identify the assigned RF channel should be relativelyefficient. In one embodiment, hash tables may be used for that purpose.

Alternative Embodiments

In one embodiment, a static multicast solution may allocate only asingle RF channel for multicast video streams. There may be no DBC-typeability in some systems to re-tune the CM to listen to another RFchannel. In this case, only about 40 or 50 Mbps may be available forvideo. This limits the number of TV programs that can be offered toabout 20, for SD content encoded for example with H.264 coding at 2 or2.5 Mbps. Such embodiments, while not preferred, are still operationaland provide some of the benefits described above.

In some embodiments. IPTV service may utilize a dynamic multicastconfiguration in the CMTS. In this approach, some bandwidth is set asidefor each Fibernode to carry multicast streams. The CMTS forwards onlythe multicast streams that are currently joined by subscribers in thecorresponding Fibernode. This approach is very spectrum efficient forsmall sized Fibernodes (relatively few subscribers), because although anMSO may offer 250 TV channels, only the channels that are currentlybeing viewed by subscribers in this Fibernode need to be forwarded.

In the dynamic approach, the steams therefore are not RF spanned overall Fibernodes. Each Fibernode has its own allocated set of DSDownstreams. The CMTS forwards to each Fibernode, on the allocatedDS(s), only the streams requested by subscribers on the node. Where thesame program is requested by subscribers on different Fibernodes, theCMTS replicates the corresponding streams. Still this approach generallyrepresents a significant savings of spectrum, since only steams actuallyrequested at the time are forwarded. In that regard, fewer RF channelsare needed to carry those streams. We have described several embodimentsin the context of using IGMP messaging. The concepts of the presentdisclosure can also be implemented using other signaling mechanisms,including but not limited to PCMM, PacketCable Multimedia protocols. Inthe PCMM framework, an Application Manager provides an interface topolicy server(s) for the purpose of requesting QoS-based service onbehalf of a subscriber or a network management system. It maps sessionrequests to resource requests and creates policies. A policy server actsas a policy decision point and policy enforcement point and managesrelationships between application managers and cable modem terminationsystem (CMTS) devices. A PCMM system can be arranged to implement cableIPTV services as disclosed herein by using the PCMM signaling mechanismsinstead of IGMP messaging. In such cases, a client requests a multimediaservice from an application manager. The application manager relays therequest to a policy server. The policy server is then responsible forprovisioning the policies on a CMTS device.

Most of the cable plant equipment discussed above comprises hardware andassociated software. For example, the typical CMTS. EQAM or CM is likelyto include one or more processors and software executable on thoseprocessors to carry out the operations described. We use the termsoftware herein in its commonly understood sense to refer to programs orroutines (subroutines, objects, plug-ins, etc. etc.), as well as data,usable by a machine or processor. As is well known, computer programsgenerally comprise instructions that are stored in machine-readable orcomputer-readable storage media. Some embodiments of the presentinvention may include executable programs or instructions that arestored in machine-readable or computer-readable storage media, such as adigital memory. We do not imply that a “computer” in the conventionalsense is required in any particular embodiment. For example, variousprocessors, embedded or otherwise, may be used in equipment such as thecable plant components described herein.

Memory for storing software again is well known. In some embodiments,memory associated with a given processor may be stored in the samephysical device as the processor (“on-board” memory); for example, RAMor FLASH memory disposed within an integrated circuit microprocessor orthe like. In other examples, the memory comprises an independent device,such as an external disk drive, storage array, or portable FLASH keyfob. In such cases, the memory becomes “associated” with the digitalprocessor when the two are operatively coupled together, or incommunication with each other, for example by an I/O port, networkconnection, etc. such that the processor can read a file stored on thememory. Associated memory may be “read only” by design (ROM) or byvirtue of permission settings, or not. Other examples include but arenot limited to WORM, EPROM, EEPROM, FLASH, etc. Those technologies oftenare implemented in solid state semiconductor devices. Other memories maycomprise moving parts, such a conventional rotating disk drive. All suchmemories are “machine readable” or “computer-readable” and may be usedstore executable instructions for implementing various embodiments ofthe present invention for mail piece sorting and related operations.

A “software product” refers to a memory device in which a series ofexecutable instructions are stored in a machine-readable form so that asuitable machine or processor, with appropriate access to the softwareproduct, can execute the instructions to carry out a process implementedby the instructions. Software products are sometimes used to distributesoftware. Any type of machine-readable memory, including withoutlimitation those summarized above, may be used to make a softwareproduct. That said, it is also known that software can be distributedvia electronic transmission (“download”), in which case there typicallywill be a corresponding software product at the transmitting end of thetransmission, or the receiving end, or both.

Having described and illustrated the principles of the invention in apreferred embodiment thereof, it should be apparent that the inventionmay be modified in arrangement and detail without departing from suchprinciples. We claim all modifications and variations coming within thespirit and scope of the following claims.

The invention claimed is:
 1. A method for delivering digital videoprogramming via a cable system network, the method comprising: receivingat least one digital video programming input stream at a cable systemhub; assigning each received input stream to an RF channel fordownstream delivery; spanning the assigned RF channels over multiplefiber nodes of the cable system network using the cable system hub;forwarding each input stream over the assigned RF channel for multicastdownstream delivery to subscribers; receiving a video stream requestsent from a subscriber equipment to an application manager using PacketCable MultiMedia (PCMM) signaling in a PCMM architecture environment;and the application manager informing the subscriber equipment of amulticast address corresponding to the video stream request, enablingthe subscriber equipment to use the multicast address to receive anddecode the corresponding input stream that is forwarded over theassigned RF channel as a multicast data stream.
 2. The method of claim 1including spanning the assigned RF channels over a selected subset ofthe fiber nodes of the cable system hub service area.
 3. The method ofclaim 1 including selecting a number of RF channels to assign for videoinput stream delivery responsive to the number and bitrates of the inputstreams.
 4. The method of claim 1 including spanning the assigned RFchannels over all of the fiber nodes of a service area of the cablesystem hub using static multicasting.
 5. The method of claim 1 andfurther comprising: identifying the RF channel to which a selected inputstream of the received video stream request is assigned; and commandingthe subscriber equipment to tune to the identified RF channel in orderto receive the selected input stream.
 6. The method of claim 5 wherein:the video stream request from the subscriber equipment is received inthe form of an Internet Group Management Protocol (IGMP) message; andthe command to tune the subscriber equipment comprises a Dynamic BondingChange (DBC) command.
 7. The method of claim 6 wherein: the IGMP messageoriginates in a set-top box coupled to a cable modem (CM); and the DBCcommand is directed to the CM associated with the set-top box.
 8. Themethod of claim 1 and further comprising: relaying the video streamrequest to a policy server; and the policy server provisioning the cablesystem hub for forwarding a requested input stream of the video streamrequest over an assigned RF channel for downstream delivery tosubscribers.
 9. The method of claim 1 wherein the foregoing steps areexecuted in a DOCSIS-3.0 compliant, integrated or modular Cable ModemTermination System (CMTS) and at least one of the input streams carriesIPTV television programming.
 10. An apparatus comprising: a video outputinterface for output of video content to a display or recording device;an interface for connection to a cable modem device; a user interface toenable user selection of a desired video programming stream; and aprocessing device configured to: map the user selected video programmingstream to a corresponding multicast group address; send a requestupstream via the cable modem device interface to request the userselected video programming stream, the request including identificationof the corresponding multicast group address; and receive the requestedvideo stream as a multicast data stream having the multicast groupaddress via a cable modem and processing the requested video streambased on the multicast group address to deliver decoded content to thevideo output interface; wherein the processing device is configured tostore television station-to-multicast group address mappings.
 11. Theapparatus according to claim 10, wherein the apparatus comprises a PC,portable device, set-top box, or other IP-enabled device capable ofconsuming digital video data.
 12. The apparatus according to claim 10,wherein the processing device is configured to send an Internet GroupManagement Protocol (IGMP) message to request the user selected videoprogramming stream.
 13. The apparatus according to claim 10, wherein theprocessing device is configured to send Packet Cable MultiMedia (PCMM)signaling to an application manager to request the user selected videoprogramming stream.
 14. A Cable Modem Termination System (CMTS)comprising: a network interface to receive multicast IP video inputstreams; and a processing device configured to: store a correspondingmulticast group address for each IP video input stream; select at leastone of the IP video input streams and assign each selected IP inputstream to a corresponding RF channel for downstream delivery; span thecorresponding RF channels downstream to a selected set of Fibernodescoupled to the CMTS for multicast downstream delivery to subscribers;receive a message requesting a selected one of the IP video inputstreams; and responsive to the request message, issue instructions tocause a cable modem (CM) associated with the request message to tune itsreceiver to the corresponding RF channel assigned to carry the selectedIP video input stream, enabling the cable modem to use the correspondingmulticast group address to receive the selected IP video input streamthat is forwarded over the assigned RF channel as a multicast datastream.
 15. The CMTS according to claim 14 wherein: the CMTS issubstantially DOCSIS 3.0 compliant; the request message comprises anInternet Group Management Protocol (IGMP) message; and the instructionsto the CM comprise a dynamic bonding change (DBC) request message tocause the CM associated with the request to tune its receiver to thecorresponding RF channel assigned to carry the selected video stream.16. A method for a cable subscriber to receive IPTV programming,comprising: at the subscriber premises, selecting a desired videoprogramming stream; at the subscriber premises, mapping the video streamselection to a corresponding multicast group address; at the subscriberpremises, transmitting a request message that includes the correspondingmulticast group address; at the subscriber premises, receiving amulticast address responsive to transmitting the request; at thesubscriber premises, tuning a receiver to an RF channel using thereceived multicast address to receive the selected video stream as amulticast data stream; and at the subscriber premises, decoding thereceived video stream for display of the selected video stream.
 17. Themethod according to claim 16 wherein said receiving further comprisesreceiving a downstream message originating from a Cable ModemTermination System (CMTS), wherein the downstream message includes themulticast address and identifies the RF channel that includes theselected video stream.